Stability Analysis of Double-Arch Tunnels Considering the Spatial Variability of Rock Parameters

Relying on a highway double-arch tunnel, the influence of the spatial variability of the surrounding rock parameters on the construction stability of the double-arch tunnel was studied by the method of finite element limit analysis combined with stochastic analysis. Firstly, the rock was regarded as homogeneous material, and the deterministic analysis was carried out. The stability coefficients of each excavation stage during the construction of the second tunnel were calculated by the finite element limit analysis. The failure mode and plastic zone distribution of the tunnel were explained. The most critical excavation stage of the construction was obtained. Then, the influence of the factors including coefficient of variation and correlation length on the stability coefficient and plastic zone distribution of the double-arch tunnel in the most critical excavation stage was analyzed using stochastic analysis. Comparing the distribution of stability coefficients obtained by stochastic analysis with the deterministic analysis results, it can be seen that even if the rock material strength reached the confidence rate commonly used in engineering, the results from deterministic analysis still overestimated the engineering safety to a certain extent, which showed the limitations of the deterministic analysis. Finally, the failure probabilities of the tunnel and recommended standard values of rock strength parameters in this project were obtained, with the spatial variability of rock parameters considered. The methods and conclusions of this paper show the importance of considering the spatial variability of the surrounding rock parameters in the tunnel design, which can provide a reference for the design and construction of similar projects.